1. Field of the Invention
This invention relates to a developing apparatus mounted in an image forming apparatus such as a photocopier or printer and, more particularly, to a developing apparatus having a sheet preventing a developing agent from leaking out of an opening formed at a developing sleeve.
2. Description of Related Art
Referring to FIG. 14 and FIG. 15, a conventional developing apparatus is described. FIG. 14 is a cross section showing a conventional developing frame; FIG. 15 is a diagram showing an end of a developing roller when viewed from Arrow X direction in FIG. 14.
As shown in FIG. 14 and FIG. 15, a prior art has been disclosed in which an elastic member made of a material, such as felt or rubber, is used as a sealing member 114 for sealing a gap between a developing frame 112 and a developing agent carrier, or a developing roller 109c, at the opposite ends in the longitudinal direction of the developing roller 109c in order to prevent toner from leaking out through the gap between the developing frame 112 of the image forming apparatus and the developing roller 109c toward the end in the longitudinal direction of the developing roller. It is to be noted that although in FIG. 14 it is depicted that there is a gap g between the developing roller 109c and the sealing member 114, this gap g exists only where a magnetic sealing member as described below is used as the sealing member 114 and does not exist where a sealing member of a contact type, such as a felt or rubber is used. Sealing below the developing roller 109c is performed by contacting, with the developing roller 109c along the longitudinal direction, a tip of a sheet member 115 formed at the developing frame 112. An end of the sheet member 115 in the longitudinal direction is sandwiched between the developing roller 109c and the sealing member made of a material, such a felt or rubber, to prevent toner from leaking out of the end in the longitudinal direction. Rotation torque of the developing roller 109c is, in this situation, increased due to sliding contact between the developing roller 109c and the sealing member during developing operation.
A sealing member, or magnetic sealing member, has been known, as a sealing member 114 disposed at the end of the developing roller 109c, in which a magnet or magnets are placed with a very small gap g along an outer periphery of the developing roller to seal the toner as a magnetic body by magnetic force from the magnet or magnets, as shown in FIG. 14 and FIG. 15(b) to reduce the rotational torque. In this situation, the developing roller 109c is not in contact with the sealing member 114, and the gap g exists as shown in FIG. 15(b). The developing roller 109c therefore does not slide on the sealing member 114 during developing operation, thereby reducing the rotational torque of the developing roller 109c, and thereby rendering extendable the duration period of the developing roller 109c. Such a sealing member is popularly used because it enjoys a merit such that it can be assembled more easily to the developing frame than other sealing members made of felt or rubber.
In a case where such a magnetic sealing member is used, however, the toner may eventually enter in a space between the developing roller 109c and the sheet member 115 as shown in FIG. 15(b) because the sealing member 114 and the developing roller 109c are not in contact with each other. The toner may deposit on the sheet member 115, and a phenomenon h that the deposited toner pushes down the end of the sheet member 115 occurs. If such a phenomenon h occurs, the sealing capability at the end of the developing roller is reduced, and the toner may leak out of the end of the developing roller.
To prevent such a falling-down phenomenon at the end of the sheet member 115, an apparatus is formed with a contact auxiliary member for the sheet member arranged on an inner side in the longitudinal direction of the developing roller with respect to the magnetic sealing portion as disclosed in Japanese Patent Application Publication No. Heisei 11-13374. However, with this apparatus, it is turned out that toner leaking to the exterior of the apparatus exists upon passing through a gap between the auxiliary member and the developing frame and passing through a gap between the magnetic sealing member and the developing frame. Furthermore, another toner leaking to the exterior of the apparatus also exists upon passing through a gap between the sealing member and the magnetic sealing portion.